The synthesis of new 3,4-(bisaryl)-1,8-naphthalimide and 2,3-(bisaryl)-7 H-benzimidazo[2,1-a]benzo[d]isoquinolin-7-one compounds and an investigation of their photochromic properties

Three new photochromic compounds, 3-(2,5-dimethyl-3-thienyl)-4-(2-phenyl-5-methyl-4-thiazolyl)-l,8-naphthalimide (1-O), 2,3-bis(2-phenyl-5-methyl-4-thiazolyl)-7H-benzimidazo[2,1-a]benzo[de]isoquinolin-7-one (2-O), and 2,5-dimethyl-3-thienyl)-7H-benzimidazo[2,1-a]benzo[de]isoquinolin-7-one (3-O), were synthesized and their photochromic properties were studied. Compound 1-O was synthesized by two consecutive Suzuki coupling reactions using 2,5-dimethylthiophene-3-boronic acid and 5-methyl-2-phenylthiazole-4-boronic acid. Photochromic compounds 2-O and 3-O were prepared by multistep reactions starting with 3-iodo-4-bromo-1,8-naphthalic anhydride and 2,5-dimethylthiophene3-boronic acid or 2-phenyl-5-methylthiazole-4-boronic acid. All photochromic compounds showed a color change from colorless (or light yellow) to blue-green, purple, or orange colors (depending on the nature of the structures) on exposure to UV light at 365 nm in ethyl acetate solutions. The colored solutions can be reversed to the original colorless (or light yellow) solution by exposure to visible light at 530 nm.